The most important ingredient in Windows 10's success during its first 12 months wasn't even a product feature, analysts said today as the operating system completed its freshman year.

"It was the fact that Microsoft was willing to learn from its mistakes, then make course corrections," Steve Kleynhans of Gartner said when asked to pinpoint Windows 10's most significant accomplishment. "There was a lot more of that with Windows 10. Microsoft made subtle adjustments, like the pace of updating the OS for enterprises, and they eventually softened on some of the more aggressive techniques for [the] Get Windows 10 [upgrade campaign]."

Ezra Gottheil, an analyst with Technology Business Research, echoed Kleynhans. "I can answer that with one word: 'listening,'" said Gottheil when asked the same question about 10's first 12 months.

Microsoft launched Windows 10 on July 29, 2015, and since then has convinced customers to put the operating system on more than 350 million devices, a record adoption pace. But the process of creating, updating, modifying, tweaking and upgrading Windows 10 ended up being more important in the eyes of experts than the OS itself.

"To make a better product, you have to become incredible empathic, which is what Apple does, or poll and collect feedback and listen, and at each step knock off the rough spots," said Gottheil. "It's a little inelegant, but if you don't do bad things, what's left is pretty good.

Microsoft chose the second path, said Gottheil, and for a good reason: "They don't have a lot of empathy for most end users," he said. "So that's what they did with Windows 10."

The result? "It's a lot smoother product than Microsoft has produced in many years, or perhaps ever," he argued.

Kleynhans concurred. "The Windows 10 Anniversary Update is a much more polished product than Microsoft shipped last year. It's polished in ways not even thought of last year. I like that feeling that they're being responsive."

Microsoft's transparency within Windows' development has waxed and waned, then waxed again, over 30 years. The regime run by former executive Steven Sinofsky was the waning part of that cycle -- Windows 8 was developed under tight secrecy -- but Microsoft loosened up with the skipping-a-numeral successor.

Considerable credit to the listen-learn-release model's success must be given to Windows Insider, the preview program Microsoft has run for nearly two years. Feedback from Insiders, the company said incessantly, was crucial to guiding 10's development. But analysts also called out other sources, notably the largest and most important corporate customers, who aren't shy about giving the vendor a piece of their minds. "There's lots of feedback that isn't as visible as Insider," Kleynhans said.

Yet Microsoft didn't sail through the year without missteps and blunders; plenty bedeviled Windows 10, even as it garnered accolades from reviewers and hundreds of millions of users.

"They had hoped to get more people to upgrade than they did," said Kleynhans, pointing out Microsoft's recent retreat from a goal of putting Windows 10 on a billion devices by mid-2018. "And they didn't get the totally positive spin in the press that they were expecting," something that curtailed upgrades on the part of people who otherwise would have pulled the trigger.

Among the things mishandled, Kleynhans highlighted the concerns over Windows 10's aggressive telemetric data collection and the even-more-combative upgrade campaign.

Gottheil focused on the latter when asked whether any false moves came to mind. "I'd say the whole 'We're going to fool you into upgrading,'" he said, referring to the deception Microsoft practiced between March and June.

"This was Microsoft saying, 'We know what's best for you,'" Gottheil said of the initial stance.

But that didn't stop him from praising Windows 10's debut year. "I'd give it an A-," Gottheil said. "There are still some hiccups, but doubling down on Cortana and adding Ink is important for the long term."

Kleynhans marked Windows 10 with two grades, not one.

"Windows 10 is a really solid product," Kleynhans said. "But the messaging and PR and general handling of all that detracted. The product deserves an A, Microsoft has provided some good updates and 350 million [copies installed] is an outstanding number. But Microsoft's handling of Windows 10, that was a C or even C-. So overall, B for the first year."